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Tech101 – Optical Fiber – Care and Safety

06/21/2014

Optical Fiber is what connects the Internet and our Data Centers, it is everywhere and it is important to know how to correctly handle it. This post is about how to care for optical fiber and how it can injure you.

Multi-Mode is used in the Data Center (short distances) for connecting routers, switches, storage and servers together (so you would see a lot of Blue and Orange fibers in your overhead cabling trays).

Single-Mode is used by Service Providers (for the greater distance) for connecting SDH, SONET, DWDM, CDWDM, Metro-Ethernet, Internet Routers and Underground/Submarine Cable systems together (so you would see a lot of Yellow fibers in your overhead cabling trays).

In the Enterprise Data Center, any yellow fibers that you would see will probably connect to your Service Provider or your own dark fiber equipment.

Optical Fiber Connector types: LC, SC, MTRJ, ST and FC

Optical Fiber Safety

NEVER, EVER PUT AN OPTICAL FIBER TO YOUR EYE TO “SEE” IF A SIGNAL IS THERE!

This is because optical fibers connect to active laser transmitters that will burn your retina and damage your eyesight.

It is also possible for a sliver of optical fiber glass (from poor termination procedures) to transfer from your fingers into your eyeball (I have never witnessed this, but on many master cabling courses, it is mentioned).

Checking for Signal – Use an Optical Power meter that measures the received power to ensure it is within specification

Poor man’s Power Meter, use the Camera Function of your Smart Phone to see if there is a signal (I think this only works for Multi-Mode 850nm)

Optical Fiber Care and Handling

If you have fiber in your Data Center and you are managing that fiber (and copper cabling) using cable ties (plastic zip lock type) that pack the fiber into tight bundles under the tiles, then you may want to consider overhead cable trays, patch panels and Velcro fasteners.

Optical fiber is incredibly strong, durable and flexible (particularly when longitudinal forces are applied), however extreme lateral forces will break the fiber. So it needs to be handled gently and installed with a turn radius of 7+ cm.

The worst thing that you can do to a fiber is create a loop and pull both ends until the loop disappears, this will shear the glass.

I mention copper Ethernet cabling (eg. CAT5E, CAT6A, CAT7) because when you crush or pinch the cable, you increase cross-talk and reduce the functional throughput of the cable. This is because an Ethernet cable is constructed of four twisted pairs with different twist rates to reduce cross-talk between them, if you damage the physical twist construction, it reduces the electrical performance of the cable.

Wiping the end of an optical fiber connector on your trousers or shirt is not going to clean it, in fact, it will make it worse.

Cleanliness – use the proper fiber cleaning kits (eg. CLETOP) for cleaning the male and female connectors of optical fibers and transceivers.

Use Optical Microscopes with FILTERS and/or FILTERED safety classes when inspecting fibers with an UNFILTERED scope.

When connecting systems together using Optical Fiber, you need to ensure that the transmitted power does not exceed the “Maximum Receive Power” of the equipment. If it does, you need to install an Attenuator or risk degrading the receiver. This is particularly true for Service Provider equipment (Yellow Fiber).

Here is a picture of CLETOP fiber cleaners (male and female) and a WWG Optical Power meter: